Anyone who ever bought a bad copy of a lens, (regardless of brand), will appreciate that Sigma will be testing each and every lens they make. This is very good news!

“Now we have built our own MTF testing system, based on the 46 megapixel Foveon Merrill sensor used in the latest cameras. This allows a much better MTF test and we can put a lens through in just five minutes.
As a result, we have started testing all the lenses produced, not just a sample. In future any Sigma lens you buy will have been MTF tested and certified.”
Graham Armitage of Sigma UK